On all engines with EPR indication, you will find that during descent with engines at idle, the EPR indicated is less than 1.00.
It can be as low as 0.80.
And with regards to negative thrust, I would rather call it drag.
And since the pressure at the intake is greater than at the exhaust there must be "negative thrust".
Even on the good old JT9D, where the PT7 probes are located in the core engine exhaust.